Dualitytale
by Twilight Master Emerald
Summary: (Solo work, Lemon warnings,some characters will be genderswapped.) What if there was an older sibling to Frisk (Gender still Pending) who fell into the underground and thanks to a unique property of their soul that they alone had acquired during the fall into the magical world, this power could change everything many know about souls and how relations with monsters can be changed.


**The scene showed TME as he walked by some trees in a snow filled area while he wore a cloak to hide his identity before he noticed the readers.**

"**Oh hello everyone, sorry for the wait and sorry for the hold up with new stories, figured I could try and make a new undertale story of sorts, the title maybe odd but let's just say that I checked…. And there are three stories titled Dueltale and I didn't want to be called a copycat…" TME said and sweatdrops from that before he clears his throat.**

"**Anyway this is sort of a what if on the Undertale story like all AU's and AU based stories… now I'll have to check on if this story was done… but what if there were more Skeletons in Snowdin and what not alongside with more monsters to help with variety, even OC siblings to current Monsters and maybe a few Fem versions of certain Canon monsters... there will be lemons in later chapters and all subjects in lemons are 18 or older so don't worry about legal age... and what if Sans and Papyrus had a sibling who for certain reasons run into a certain human who has a strange ability before the Undertale timeline?... one that will play into the Undertale timeline in ways no one may expect… after all this title is more than just a way to tell how the story could go… but why spoil more when the story can tell you… as the title says this is a prologue so the real story starts when the OC is introduced… right…about... now." TME explained while one eye gave a green glow before he vanished from sight as the scene shifts...**

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**Two years before Undertale Timeline/ Entrance to Mt. Ebbot**

Like how most stories with a beginning start… this one showed a massive forest surrounding a massive mountain called Mt. Ebbot… rumors tell of monsters and other beings probably worse being sealed inside… though even if the rumors were true in the past with towns and cities involved between the war with Monsters and Humans, this tale was now more than a fantasy filled legend for most which resulted in two men standing in front of a large forest with a path leading in it while one pats a different man on the back.

"Come on Emerald, we all know that only kids get lost on Mt. Ebbot… at least that's what we were told years ago as kids to keep us in line when our parents threatened us to keep us in line... so you should be fine since you turned 18 a few months ago, it's just a trip into the cave and back after grabbing a few things there to show you have been there as proof and you get 100 bucks." A man said with an amused look on his face to another man near him who looked nervous... But the man making the dare knew Emerald would do anything for cash for the right reasons and this was for his siblings up-and-coming birthday...

The two men in question were not family, not even friends, they were just people who knew one another in the town that they lived in and thanks to a dare, Emerald, a man with long brown hair, Green colored eyes, black shirt with red cargo pants and a black coat with black boots and some headphones with an SD card inside which had plenty of songs in the headphones… honestly you could mistake Emerald being dressed for either Christmas or some kind of edgy guy but that was further from the truth.

Emerald was more of a writer who wrote stuff like fanfiction and played games, listened to music, and pretty much didn't like to fight… in some cases some called him too nice and wondered if he had a few screws loose when he pretty much rarely fought back against bullies… however... he had one thing that would turn him into a surprisingly scary guy…

Mess with his family and it was like he was a different person entirely… one that would break anything in his way if his little sibling Frisk was harmed in anyway, shape, or form, and the young child had to get his brother to snap out of his rage and it really worried many when it looked like he would kill someone… at least from what they knew… even therapy and what not could not figure out what was going on besides being protective but this was… something… different...

However that was in the past, most of the time he was docile as a puppy and right now he was walking along a path up Mt. Ebbot so he could get the proof and get that 100 dollars… it was supposed to be a weird blue flower that grew at the back of the entrance of the cave, rumors said that the flower gave a blue light and seemed to repeat the last things said if you said something in it… if it wasn't for the rumors children go missing, many would try and go up the mountain to see if the rumors were true.

For a bit, Emerald keeps on walking up the path while he had a nervous look on his face while back at the entrance… the man was approached by a couple others.

"Hey man, you really going to pay 100 dollars for a flower?" One man said while the man who made the bet chuckles.

"Sure… IF he returns…. A monster like that in human skin would be better off vanishing so the rest of us can sleep safely… but if he does come back with that rumored flower, it would be cash well spent since it would mean thousands or even millions for a flower like that with the highest bidder… so win win either way… now let's get going before anyone gets wise about what we did." The man said with a cold grin on his face while the other men looked a bit nervous.

"What about his family?, won't they worry about what happened with him?" Another man said which made the cold man shrug.

"Not my problem, besides… you haven't seen what I've saw… better off if he dies there then kill someone again… I'm sure his family would thank me if they found out but that is IF… they find out… for now let's get the hell out of here and you all keep quiet." The man said while he grins at them before the other men followed him away from the Forest of Mt. Ebbot.

while back with Emerald…

He made it up the mountain without much trouble since… it was mostly a pathway up the mountain and when Emerald got to the cave… he was stunned with how… massive the cave was… it was like a giant maw just waiting to devour anyone entering which made Emerald gulp before he entered while he thought about Frisk and how happy they would be if they got that game console that they wanted… Emerald saved up 200 already… that 100 would help him get a console on sale and it even had a free game coupon that they wanted… Earthbound… he never even told his parents about this to really surprise them as well… Emerald even chuckles at the looks that would possibly on their faces as a result.

So Emerald, after he calmed down, keeps walking and when he got deep in the cave he saw massive opening in the floor with his prize in sight… on the other side of the pit and the only way across was a thin ledge.

Emerald gulped again and took a few breaths before he placed his headphones on his head and starts to play some music to cope with this tense situation and he approached the ledge and with his back pressed up against the wall… he starts to edge his way to the flower inch by inch… and everything went well till his foot sliped halfway and he barely caught himself by digging his fingers into the softish wall and pants for breath quickly while he saw rocks from his lack of a foothold fall into the seemingly endless abyss…

Meanwhile deep into the hole…

"Hmhmhmhm…" A female voice hummed while they attend to the flowers deep in a place with only one exit out… now one would think this was Toriel… Caretaker of the Ruins… but no, this was a Skeleton woman who contrary to what many would say, was a beautiful woman with sharp cheekbones, and a nice dress with a watering can while she watered the flowers… and the green dress she wore showed she had a shapely body even if she technically was only just a skeleton and wore green boots.

Now one would ask how this was possible when most skeletons died in the war with the humans… well that is the key thing… MOST skeletons did die but thanks to some effort from a few few skeleton elders when the war happened, many skeleton children were moved to Mt. Ebbot in advance which meant that all the skeletons in the Underground were the children of the adults who dies and grew up while they cared and looked out for one another, and aside from the iconic Papyrus and Sans who popped up out of nowhere, they had a third with them and while Sans and Papyrus were children barely 3 and 5 respectively… Sans carried a small bundle of energy who for a Skeleton who normally named themselves for a Font, this one was named different since she could naturally speak in many fonts but made them sound… neat... if that can be a word.

Her name was Libertarian… and she was like the middle ground between Sans and Papyrus with her goals, stats, even her abilities with colored magic.

You see she was proficient with Green magic like no other and it was mainly used in the healing magic arts, she normally used it to heal Papyrus after his training with Undyne and to try and keep Sans above 1 HP with her buff to allow one to have a shield of sorts, granted the total depended on the persons HP total, so for Sans who had one, he had a shield normally around him that had 10 HP, but considering how low his HP was normally, that was a serious boost while others like Undyne or Papyrus has a monstrous leap, so much so that she was widely liked by others in various areas of the Underground not only for her abilities.

And to some monsters, she was a beauty among monsters so she normally visited the Ruins with her brother Sans, but unlike him, Libertarian managed to talk the caretaker of the Ruins Toriel the Queen of monster… or Ex-Queen, to let her in so she could give her company when Sans left and right now she was helping Toriel with watering the plants and was humming a tune as she did so… but she noticed a few rocks falling near her which spooked her and when she looked up… her eye sockets widen when she saw at the very top, someone edging along the ring of the pit and her green colored dot like eyes shrank in worry when she saw the person nearly falling again when he tried to reach for something.

Back with Emerald…

He was trying to not fall when he reached for the flower… he could see that 100 dollars being handed to him and aside from a few near slips, nothing happened yet… but when he grabbed the flower… it seemed to… shift somehow before it was pulled from the ground all too easily and thanks to that momentum… Emerald starts to fall with a scream and Libertarian dropped her watering can when she covered her mouth when she saw Emerald's falling form… however thankfully and thankfully for her… her attribute with Green magic made her a kind woman… some would say too kind which was seen when she ran forward to try and catch Emerald since his landing was far off from the flowers which she heard was the main reason why the previous children who fell here survived… without that and Emerald would be nothing more than a stain on the ground.

Now if some third party was watching some may wonder what happened next or why it happened because when Libertarian tried to catch Emerald, she used her magic to try and grab his soul to either slow or stop his fall and used her magic on herself as well to brace her body to catch Emerald when that didn't work… however what no one expected was Emerald crashing into Libertarian like a freight train and both Monster and human crashed to the ground and blacked out right then and there…

But unaware to anyone, thanks to Libertarian's magic… an unexpected thing was happening to Emerald thanks to how much magic was being poured into him while Libertarin's magic was on full burst for quite a bit while she was knocked out so she couldn't stop the flow and… Emerald's soul… which was red for Determination oddly enough given his personality was normally a kind was, was starting to ink with green from Liberation and the inked parts… cracked and shift around while Emerald, who was out cold grit his teeth as his body starts to change…

First his flesh starts to fade from existence like he was turning transparent and only his bones were left with his clothing and headphones were still on his head while his partly morphing soul was seen which showed he was still alive… somehow, his closed eyes which vanished turned into pin prick like pupils that had a mix of red and green before that light fades to show a complete knock out was seen on his vacant skeleton face.

Libertarian's body starts to shift as well much to any onlookers shock if they were there… her body starts to form… flesh on her skeleton like figure and she had ebony colored skin, full sensual lips, more shapely breasts and hips hidden by her outfit and the skirt, and thanks to the now seen legs being seen to her boot covered feet, she had sexy legs which had no blemish at all on her skin.

Time went to a few hours later with a large goat woman like monster entering the area after she wondered what was keeping Libertarian, she wore a white and purple robe while some kind of symbol was on the front.

Her name was Toriel Dreemur… Ex- Queen of the Monsters when she left him since she couldn't stand the killing of children in the past.

Anyway aside from the canon timeline with Toriel and the occasional visiting Libertarian added on that, she was the exact same caring woman who everyone knew and loved though she did keep her location a secret from many besides Libertarian and Sans, though for Sans, he mainly just stayed at the door to tell jokes and helped his sister enter the ruins after making sure the coast was clear.

Anyway long story short, when Toriel checked in on Libertarian, she was shocked to see a odd looking skeleton on top of a human woman shockingly enough who… wore Libertarian's outfit… and while she was confused as hell, she did see that they both looked knocked out for some reason and rushed over to them to check on them before anything else could happen.

"Oh my, are you two alright?, are any of you even awake?" Toriel said to see if either of them were awake… though when she got nothing for a bit, she picked both of them up and left the flowerbed area and ran through the Ruins while disabling her puzzles at a record pace while she was careful when she carried the duo.

When she got to her place deep in the ruins, she placed Emerald in one room to rest while she placed Libertarian in another and though she wondered about the outfit that, to Toriel, a strange human was wearing, she didn't try and force the Human awake since didn't know the story behind the outfit.

Toriel then went to cook some food so when the two would awake, she could make sure they were at full health and what not so she could get a clear conversation started.

**3 hours later…**

"U-Ugh…" Emerald groans as he slowly opened his eyes… or sockets to show white pupils while he didn't know anything about his new form… but he did feel like… something... was…. off about him for some reason… maybe the fall did more damage than he thought… which could explain why he was seeing a ceiling instead of the top of the hole.

"D-Damn… didn't expect that." Emerald muttered and sat up while he held his head while his slightly blurred vision starts to clear when he felt his light head sort itself out but before he could think much on how he survived, he heard knocking on the door.

"Excuse me, I heard noises in here, are you awake?" A female voice asked while Emerald blinked a few times.

"U-Uh… yeah… I think so." Emerald said when he wondered where he was as he looked around the room and saw that he was in some kind of kids room and the bed barely held his body… and when he looked he saw that his body looked fine… though… did he seem… skinnier?

Though before he could check to be sure since it was dark for the most part, the door to the room opened and Emerald heard a voice.

"Well that's wonderful, I was hoping that was the case." Emerald heard before he looked… and before he could speak… his jaw dropped greatly and his eyes widen to comical proportions when he saw a tall female looking goat like woman entering the room and when his mind fully registers her, and her confused look at Emerald's face… Emerald breathed in to get ready to scream in fright… but was beaten when a female scream was heard which shut him up before he could even yell and he and the goat woman flinch and cover their ears from how loud the scream was… though… Emerald did wonder why he couldn't feel his ears… did they go numb if he slept wrong?

Though the goat woman looking worried did get Emerald's attention before Emerald gets up from the bed which got her attention.

"Come on, we should check on who screamed." Emerald said to try and get some kind of order here and while he was shocked about the Goat woman, he did see that she had a kind look in her eyes while the Goat woman smiles at Emerald, his thoughts worried on who screamed.

"Very well, let's head to my room then, I'm Toriel, Caretaker of these Ruins and I found you and a Human female laying in the flowerbed area… though I am wondering why a Skeleton like you was here and with a Human in the ruins… and that human looked like a full grown woman…" Toriel said while she unknowingly left a stunned Emerald behind when he blinked a few times.

"S-Skeleton?" Emerald said with a confused tone to his voice before he looks at his hands and… his jaw dropped again since thanks to the light from the open hall… Emerald saw boney hands and he shakingly raised them to his face and felt it carefully and his pupils turned green and red in shock when he could feel the lack of a face…

Now one would think Emerald would freak out but the scream from the other room did cause his eyes to widen… if he was a Monster like the rumors on Mt. Ebbot… then if that woman was a Monster who was turned Human… then wasn't it his fault somehow?

That caused Emerald to grit his teeth and force his fear and frustration down so he could think clearly… he needed to if he wanted to survive if some monsters down here wanted to kill him… anyone who came to Mt. Ebbot never returned after all… or did they turn into Monsters and wind up down here like him as well?

Though he put those thoughts away for now to follow Toriel out of the room and saw her knocking on a nearby door which Emerald followed her to.

"Excuse me, we heard you scream, are you alright?" Toriel said before she entered the room and Emerald followed suit but Toriel was surprised when the human ran up to her and hugged her around the waist.

"T-Toriel!, I... don't know what's going on!, I went to water the flowers and I helped a Human from falling to their death and now I'm looking like a human now!, just what is going on!" Libertarian said while Toriel was greatly confused while Emerald's pupils vanished when he realized that this human… was the skeleton woman from earlier… it was a bit blurry in his mind but he remembered vaguely as he fell, for a moment during one of the turns, that he saw a skeleton in an outfit like that… granted he did have a green and red blush on his skull like head a moment later when this woman looked pretty good to him… which made him shy for a moment but shook his head when thoughts like that could get him in trouble since he wasn't a ladies man… he could barely talk with them when he was human and he was a stuttering mess most of the time.

Though he was brought out of his thoughts when Toriel looked confused.

"U-Ummm… not sure what you mean by that dear… I mean... yes I know a Skeleton woman by the name of Libertarian who wears a dress like yours when there to water the flowers... but all I saw at the Flowerbed area was this handsome skeleton man and you knocked out on the ground, who are you by the way?, I'm Toriel, Caretaker of the ruins." Toriel said which made Emerald blush with his green and red blush when he got a complement by the Goat woman while the woman, at least, Libertarian, from Emerald's guess from a process of elimination if no one else besides Toriel was there to bring them here, looked at Toriel with a stunned look on her face and cries while Toriel looked more confused.

"U-Um… Mrs… Toriel was it?... I think I can explain the confusion… somewhat… I'm still confused myself on what's going on but uhhh… I believe that's Libertarian who's crying her eyes out… you said so yourself that you found the two of us in the Flowerbed area… whatever that is… I mean unless there was someone else, It's pretty obvious its her given the outfit right?" Emerald said while Toriel blinked a few times before she giggles a bit.

"But that's silly, I mean Libertarian is a Skeleton, not a human." Toriel said like she thought this was some kind of joke while Libertarian teared up more and Emerald had a serious look on his face.

"Because it's true… before I fell… I used to be Human and well… I'm sure what happened after that fall caused this switch but well… even if you don't believe that, you gotta admit this situation is strange in of itself." Emerald said which made Toriel blink a few times.

"W-Wait… so your… a human turned Monster?... like for real?... you are not kidding?" Toriel said which made Emerald nod his head a few times while Toriel looks at Libertarian who had tears in her eyes.

"A-And you are… really Lib?" Toriel said which made Libertarian sniff a few times and she nods her head a few times while Toriel got wide eyes when she could tell they were telling the truth.

"Oh my… but… how is this…." Toriel said while Emerald crossed his arms.

"Considering this… Lib… Liberation?... Liber…" Emerald said while he tried to remember Libertarian's name which made the former skeleton sniff a few times when she seemed calmer.

"Libertarian…. Though… friends call me Lib for short… considering things I may let you call me that… but…" Libertarian or Lib for short for ease of introductions while Emerald nods his head while Toriel just looked more confused.

"Right err… Lib… anyway unless we can talk with someone who can help us figure things out, we could be stuck like this… and unless there are other cases of humans turning into Monsters like me in the past and living here, then we could find a way to change you back if possible." Emerald said which made Toriel blink a few times.

"Um...I may not follow much about what's going on but no one else in the Underground has ever gone through a situation like this, I can assure you of that at least…" Toriel said which caused Emerald and Lib to get worried looks on their faces which caused Toriel to try and run damage control.

"B-But I'm sure we can think of something… with you two staying here… I mean Asgore and the Royal knights are looking to hunt Humans for their souls and if they see Lib like this…" Toriel said which caused Emerald to blink a few times.

"Wait… souls?, how can you hunt humans for something you can't see or touch?, it's not scientific as far as I know… then again I was a human turned into a skeleton and a Skeleton was turned into a Human somehow so what do I know." Emerald said with a half lidded look on his face while Toriel and Lib blink a few times.

"You don't know what souls are?" Toriel said while Emerald keeps on giving Toriel a half lidded look.

"Well unless I missed some lessons in the past, most people say that the soul is a state of being that every living being has and when you die, it can either go to one of the various afterlifes that one believes in depending on their religion, or to hell if you were a sinful human, same thing applies depending on the religion, not sure about the soul thing your talking about if its different here." Emerald said which really confused Emerald and Lib greatly.

"I-I see… seems all the history books don't talk about the war between Monsters and humans." Toriel said while Emerald crossed his arms.

"No, it mentions it, but it's mainly just a fable many tell where I'm from to scare kids into listening to their parents and stuff like that, there is also this flower that I heard about that was planted at the top of the hole and if I got it, I would have been paid 100 Dollars." Emerald said while Toriel and Lib tilt their heads.

"D-Dollars?" The duo said and Emerald sweatdrops.

"Well it's like currency in a nutshell… not sure if you have a currency down here but same idea." Emerald said to the duo.

"Ah, so its like gold coins." Toriel said while she got a gold coin from her pocket and Emerald sweatdrops again.

"Y-Yeah… that." Emerald said when he realized he may have trouble here if he needed to buy things.

Though Lib and Toriel didn't notice that when Toriel looks at Lib.

"Anyway… Lib… are you alright?" Toriel said when she wondered how the former Skeleton was doing.

Lib, after she managed to calm down thanks to the talk on souls and dollars, looks up at the Ex-Queen.

"W-Well… now that I have my thoughts collected… for the most part… I… feel fine, just… diferenty…" Lib said while she tilts her head a bit which gave her an adorable look on her face which made Toriel smile a little even if this situation was a bit dire.

Though Emerald clearing his throat did get Toriel's and Lib's attention.

"Anyway what's with this Asgore guy and these Royal guards trying to get souls?" Emerald asked which caused Toriel to sigh.

"That's because he is trying to break the barrier to Mt. Ebbot so we monsters can be free, but in order to do that he needs 7 human souls to do that… and unfortunately… he killed 6 children already… I… couldn't take it anymore after trying to convince him to stop so I left him and I live in the ruins now." Toriel said which made Emerald shudder when he realized why Toriel wanted Lib to stay here.

"Well now I get why you want Lib to stay here… but what if this is for good or something?, unless we find out how Lib and I can return to normal, then Lib will be in constant danger and unless she has some family, then staying here won't be a good thing for her." Emerald said which caused Lib to look shocked when she remembered that she had two brothers back in snowdin.

"Oh god… what will I tell Sans and Papyrus?" Lib said with a worried look on her face as she lets go of Toriel, placed her hands on her cheeks and worried greatly that Sans and Papyrus would freak out if they hear about this.

Though Emerald had no idea about them, Emerald tried to calm Lib down.

"Easy Lib, I'm sure we can explain things if we can prove ourselves to them, I mean they are smart guys right?" Emerald asked while Lib looked somewhat relieved.

Though… she did get a cringe like look on her face a moment later which confused Emerald somewhat.

"Well… Sans is smart even if he does love his puns… but Papyrus… well… he's a nice guy and does love his puzzles but well… he can be a bit… enthusiastic about things." Lib said while Emerald looked confused.

"Err… guess those are your brothers it seems… think they can help us or know someone who can?" Emerald asked while Toriel frowned.

"Now hold on, while I can understand getting help, what will you do when everyone finds out you are human?, and even if not, what about Lib?, can you defend her or can you even defend yourself?" Toriel asked which made Emerald opened his mouth but he closed it and opened again silently when he had no idea on even how to defend himself, he heard that Monsters are weaker than humans physically from another history book and since he had no idea about how to fight like a monster… well…

"Well… think you can teach me then?, how to defend myself I mean?" Emerald asked out of the blue which made Lib and Toriel blink a few times.

"Uh… I don't mind but it could take awhile since I'm not sure how well you can use Monster Magic." Toriel said while Emerald took a moment to breath in when he remembered his parents and Frisk.

"No worries… until I'm ready to stay alive… I'm not going anywhere." Emerald said while his eyes glowed with a green and red light which showed how determined he was as the scene fades to black with Toriel shortly starting the lessons and it would be a year before Emerald would be ready to leave the ruins.

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**(End of Prologue 1: Prologue 2 and final Prologue chapter will be worked on soon.)**


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